In conventional applications, biosensors for detecting the physiological signals are applied in large medical equipment. However, with new technical developments, wearable devices which were originally applied for medical purposes can also be the ones for the purposes of health and fitness. Because the market for wearable devices is growing, the application of biosensors to wearable devices has attracted more and more attention.
In the prior art, the method for detecting a heart rate in a wearable device is to measure the signal for the change of the vessel volume, and this signal is measured by recording and sensing the energy variation of light using photoplethysmography (PPG). Because the heart beats are periodically verified, the volume of the blood flow in the vessels per unit of cross-sectional area will change periodically. When the volume of the blood flow per unit of cross-sectional area changes, voltage signals, current signals or resistance signals will be detected by a photodetector with the variation of the volume of the blood flow. The relevant conventional techniques are described in patent applications such as CN103156591, WO2013038296, U.S. Pat. No. 8,172,761, US20090112111 and U.S. Pat. No. 5,807,267, and IEEE literature such as Hayato Fukushima et al. “Estimating Heart Rate using Wrist-type Photoplethysmography and Acceleration sensor while running” (Engineering in Medicine and Biology Society (EMBC), 2012 Annual International Conference of the IEEE, Aug. 28, 2012, p. 2901-2904.) and Zhilin Zhang et al. “A General Framework for Heart Rate Monitoring Using Wrist-Type Photoplethysmography (PPG) Signals During Intensive Physical Exercise” (IEEE Transactions on Biomedical Engineering, February 2015, 62(2): 522-531.), and a thesis such as Bennett Ames Fallow “Influence of Skin Type and wavelength on Light Wave Reflectance” (Master Thesis of Science in Kinesiology, the University of Texas at Austin, May 2012.).
However, the signals detected by the photodector may be interfered with and there is substantial noise in the signal because of the human body's motions during exercise, which causes serious distortion of the detected heart rate. Even in a motionless situation, static activities such as pressing the keys of a keyboard or writing also cause the distortion of the detected heart rate.
To overcome the drawbacks in the prior art, a method for detecting a heart rate is disclosed. The particular design in the present invention not only deals with the problems described above, but is also easily implemented. Thus, the present invention has utility for the industry.